ECG Practical

Question 1

how is the heart rate calculated

Answer 1

calculate R waves in 60 seconds (likely not to have 60 seconds of trace)

measure out 15cm of trace (use the small 1mm squares to guide you i.e x10 of the 1mm squares is 1cm) 15 cm of trace = 3 seconds of time at a paper speed of 50mm (which equals 5cm) per second

then count how many R waves are in 3 seconds

(ex. 4 R waves in 3 seconds then the number of R waves in 60 seconds must be 4 x 20 = 80 R waves) = 80 beats per min)

Question 2

how many seconds is a 1mm square on 25mm paper speed

Answer 2

0.04 seconds (not 0.02 seconds in 50 mm)

Question 3

how is the PR interval

Answer 3

count the number 1 mm boxes the PR interval takes then multiply it by 0.02s (0.04 in 25 speed)

PR interval goes from beginning of the P wave to just before Q (not the R wave) and represents conduction of depolarization across the atria

Question 4

how is the QT interval calculated

Answer 4

count the number of boxes QT takes up (mult by 0.02 if 50 or 0.04 if 25)

QT interval goes from beginning of the Q wave to the end of the T wave and represents depolarization and repolarization of ventricles